(This article was first published on SAS and R, and kindly contributed to R-bloggers)
Propensity scores can be used to help make causal interpretation of observational data more plausible, by adjusting for other factors that may responsible for differences between groups. Heuristically, we estimate the probability of exposure, rather than randomize exposure, as we'd ideally prefer to do. The estimated probability of exposure is the propensity score. If our estimation of the To leave a comment for the author, please follow the link and comment on his blog: SAS and R.
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Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).